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Manual Section... (8) - page: update-binfmts

SYNOPSIS

[options
]
--installname path spec

[options
]
--removename path

[options
]
--import
[name
]

[options
]
--display
[name
]

[options
]
--enable
[name
]

[options
]
--disable
[name
]

DESCRIPTION

Versions 2.1.43 and later of the Linux kernel have contained the binfmt_misc
module.
This enables a system administrator to register interpreters for various
binary formats based on a magic number or their file extension, and cause
the appropriate interpreter to be invoked whenever a matching file is
executed.
Think of it as a more flexible version of the #! executable interpreter
mechanism, or as something which can behave a little like "associations" in
certain other operating systems (though in GNU/Linux the tendency is to keep
this sort of thing somewhere else, like your file manager).
manages a persistent database of these interpreters.

When each package providing a registered interpreter is installed, changed,
or removed,
is called to update information about that interpreter.
is usually called from the
postinst
or
prerm
scripts in Debian packages.

OPTIONS

Exactly one action must be specified; this may be accompanied by any one of
the common options.

COMMON OPTIONS

--package package-name

Specifies the name of the current package, to be used by package
post-installation and pre-removal scripts.
System administrators installing binary formats for local use should
probably ignore this option.

When installing new formats, the
--import
action should be used instead.

--admindir directory

Specifies the administrative directory, when this is to be different from
the default of
/var/lib/binfmts

--importdir directory

Specifies the directory from which packaged binary formats are imported,
when this is to be different from the default of
/usr/share/binfmts

--cachedir directory

Specifies the directory in which binary format registration instructions
are cached, when this is to be different from the default of
/var/cache/binfmts

--test

Don't do anything, just demonstrate what would be done.

--help

Display some usage information.

--version

Display version information.

ACTIONS

--install name path spec

Install a binary format identified by
name
with interpreter
path
into the database.
After registration, this format will be used when the kernel tries to
execute a file matching
spec
(see
Sx BINARY FORMAT SPECIFICATIONS
below).

--install
will attempt to enable this binary format in the kernel as well as adding it
to its own database; see
--enable
below.

You cannot install a format with any of the names ".", "..", "register", or
"status", as these are used by the filesystem or the binfmt_misc module.

--remove name path

Remove the binary format identified by
name
with interpreter
path
from the database.
This will also attempt to disable the binary format in the kernel; see
--disable
below.

--import [name
]

Import a packaged format file called
name
or import all format files currently on the system if no
name
is given.
If
name
is not a full path, it is assumed to be a file in the import directory
( /usr/share/binfmts
by default).
See
Sx FORMAT FILES
below for the required contents of these files.

For packages, this is preferable to using the
--install
option, as a format file can be installed without
needing to be available.

--display [name
]

Display any information held in the database about the binary format
identifier
name
or about all known binary formats if no
name
is given.
Also show whether displayed binary formats are enabled or disabled.

--enable [name
]

Enable binary format
name
or all known binary formats if no
name
is given, in the kernel, thus enabling direct execution of matching files.
You must have binfmt_misc compiled into the kernel or loaded as a module for
this to work.

--disable [name
]

Disable binary format
name
or all known binary formats if no
name
is given, in the kernel, thus disabling direct execution of matching files.
You must have binfmt_misc compiled into the kernel or loaded as a module for
this to work.

BINARY FORMAT SPECIFICATIONS

--magic byte-sequence

This matches all files with the magic number
byte-sequence
Hexadecimal escapes may be included in the
byte-sequence
by preceding them with \x, for example
`\x0a'
for a linefeed.
Remember to protect such escapes with quotes or an additional backslash to
prevent their interpretation by the shell.

Also see
--offset
and
--mask

--offset offset

This is the offset of the magic/mask in the file, counted in bytes.
The default is 0.
Only valid with
--magic

--mask byte-sequence

This mask will be logically-ANDed with the string to be checked against the
magic number given with
--magic
The default is all 0xff, i.e. no effect.
Only valid with
--magic

If this option is used, a userspace detector program will be used to check
whether the file is suitable for this interpreter.
This may be used when the binary format is more complex than can be handled
by the kernel's format specifications alone.
The program should return an exit code of zero if the file is appropriate
and non-zero otherwise.

FORMAT FILES

A format file is a sequence of options, one per line, corresponding roughly
to the options given to an
--install
command.
Each option consists of a key, followed by whitespace, followed by a value.

The
package
option should be set to the current package.
The
interpreter
option should be set to the path to the interpreter that will handle this
binary format.
The
magicoffsetmaskextension
and
detector
options correspond to the command-line options of the same names.

EXIT STATUS

0

The requested action was successfully performed.

2

Problems were encountered whilst parsing the command line or performing the
action.

EXAMPLES

This format file can be used with an interpreter capable of handling Java
.class files:

NOTES

If you're not careful, you can break your system with
.
An easy way to do this is to register an ELF binary as a handler for ELF,
which will almost certainly cause your system to hang immediately; even if
it doesn't, you won't be able to run
to fix it.
In the future
may have some checks to prevent this sort of thing happening accidentally,
though of course you can still manipulate the binfmt_misc kernel module
directly.

AUTHOR

An -nosplit
is copyright (c) 2000-2002
An Colin Watson Aq cjwatson@debian.org .
See the GNU General Public License version 2 or later for copying
conditions.

You can find the GNU GPL in
/usr/share/common-licenses/GPL
on any modern Debian system.

Richard Guenther wrote the binfmt_misc kernel module.

THANKS

Ian Jackson wrote
update-alternatives
and
dpkg-divert
from which this program borrows heavily.